U.S. Code of Federal Regulations
Regulations most recently checked for updates: Jan 27, 2020
(a) General. Each room, locker, and box for storage batteries must be arranged or ventilated to prevent accumulation of flammable gas.
(b) Power ventilation. If power ventilation is required, the following must be met:
(1) The power ventilation system must be separate from ventilation systems for other spaces.
(2) Electric motors must be outside the duct and compartment and:
(i) Have an explosion-proof motor for a Class I, Division 1, Group B location; or
(ii) Be at least 10 ft. (3 m) from the exhaust end of the duct.
(3) Each blower must have a non-sparking fan.
(4) The power ventilation system must be interlocked with the battery charger so that the battery cannot be charged without ventilation.
(c) Large battery installations. Each battery room for large battery installations must have a power exhaust ventilation system and have openings for intake air near the floor that allow the passage of the quantity of air that must be expelled. The quantity of the air expelled must be at least:
(d) Moderate and small battery installations. Each battery room or battery locker for moderate or small battery installations must have louvers near the bottom of the room or locker for air, and must be ventilated by:
(1) Ventilation that meets paragraph (c) of this section;
(2) An exhaust duct:
(i) That ends in a mechanically ventilated space or in the weather;
(ii) That extends from the top of the room or locker to at least 3 ft. (1 m) above the top of the room or locker;
(iii) That is at an angle of 45 degrees or less from the vertical; and
(iv) That has no appliances, such as flame arresters, that impede free passage of air or gas mixtures; or
(3) A duct from the top of the room or locker to an exhaust ventilation duct.
(e) Deck boxes. Except for a deck box for a small battery installation, each deck box must have a duct from the top of the box to at least 4 ft. (1.2 m) above the box ending in a gooseneck or mushroom head that prevents entrance of water. Holes for air must be on at least two parallel sides of each box.
(f) Weathertight. Each deck box must be weathertight.
(g) Boxes for small battery installations. Each box for a small battery installation must have openings near the top to allow escape of gas. If the installation is in a non-environmentally-controlled location, the installation must prevent the ingress of water.